umm.js

function make_groups(str){
  // makes an array of strings, for example aabb -> [[2,'a'], [2,'b']]

  var boundaries = [];
  var groups = [];

  var current_letter = null
  for (var i = 0, len = str.length; i < len; i++) {
    if (str[i] !== current_letter){
      current_letter = str[i];
      boundaries.push(i);
    }
  }

  boundaries.push(str.length) // limit of the last boundary needs upper limit

  for (var i=0, len = boundaries.length -1; i < len; i++){
    n_of_elements = boundaries[i+1] - boundaries[i];
    groups.push([n_of_elements, str[boundaries[i]]]);

  }

  return(groups);
};


function lookSay(number){
  var groups = make_groups(String(number));
  var final_string = [];

   for (var i=0, len = groups.length; i < len; i++){
      final_string.push(groups[i][0]);
      final_string.push(groups[i][1]);
  }

  number = final_string.join('');

  return Number(number);
};

lookSay(122);